The invention relates to a transistor power amplifier having reduced switching times which is suitable for pulse operation. Amplifiers of this type are extremely useful since, compared to continuously operated transistors, they have less power dissipation and therefore a high degree of efficiency. In addition, when used in digitally controlled electrical drives, they permit predetermined rotational speeds being very accurately observed. They are used, for example, when brushless DC motors are employed as drives for magnetic disk storages or for form and type band transport in line printers which are used as output units of data processing systems.
In pulse-operated brushless DC motors if currents of more than 1 A are required to be switched at frequencies ranging from 20 to 200 kHz, short switching times are necessary for the final stage transistors of the power amplifier, in order to avoid overheating these transistors and the electrical breakdown resulting therefrom. As is known, the power dissipation occurring in these transistors depends on the magnitude of the switched current, the operating voltage, and the switching frequency. Short switching times of the final stage transistors thus permit higher switching frequencies without the aforementioned breakdown occurring.
Circuits for reducing the switching times of final stage transistors used in power amplifiers are known in the prior art. However, these circuits invariably require special additional auxiliary voltages.
The present invention, which is specifically set forth in the appended claims, overcomes these and other disadvantages of the prior art. Accordingly, an object of this invention is to provide a transistor power amplifier having reduced switching times which is suitable for pulse operation without requiring special additional auxiliary voltages.